The battle for control of the Sinaloa cartel is intensifying, and 'El Chapo' Guzmán's sons are under fire

Joaquin "El Chapo" Guzmán arrives at Long Island's MacArthur Airport on January 19 after his extradition from Mexico. Reuters

The brewing conflict between aspirants to the Sinaloa cartel throne apparently reached a new stage earlier this month when gunmen aligned with one cartel leader attacked the sons and a longtime associate of the jailed kingpin Joaquín "El Chapo" Guzmán.

According to a letter purportedly handwritten by Jesús Alfredo and Iván Archivaldo Guzmán, the attack occurred when they arrived with Ismael "El Mayo" Zambada at a meeting on February 4 called by longtime cartel member Dámaso López "on the issue of having evidence that Dámaso López ordered the kidnapping of the sons of 'El Chapo'" in August.

When they arrived at the meeting site — reportedly in Badiraguato, the Sinaloa municipality where "El Chapo" was born— gunmen opened fire on them. According to the letter, which was originally published by the Mexican journalist Ciro Gómez Leyva, some of the bodyguards were killed instantly.

The brothers "realized they were betrayed by el licenciado Dámaso López, trying to kill them so as to end" the Guzmán family at the root, the letter says, referring to López as "licenciado" because he has a law degree.

"This, in fact, did happen," Mike Vigil, a former chief of international operations for the US Drug Enforcement Administration, told Business Insider, citing conversations he had with Mexican security officials.

A Mexican marine looks at the body of a gunman next to a vehicle after a gun fight in Culiacan on February 7. (AP Photo/Rashide Frias)

"Apparently, [López] called for an important meeting, and when they showed up they ran into a barrage of bullets from at least five or six or individuals," Vigil said. "They killed some of their bodyguards, but they were able to [get] away."

Guzmán's sons and Zambada fled, but they encountered other armed men, who had orders from López to kill them. The letter says they traveled several kilometers before finding a small town, where their wounds were treated — though it's unclear if "El Mayo" Zambada was wounded.

José Refugio, a Mexican lawyer who represents "El Chapo," acknowledged the letter in an interview with Mexico's Radio Formula.

"I had knowledge of this. I knew of that letter, and I knew they made that letter," he said. "But it did not arrive through me."

The Dámaso López referenced in the letter appears to be Dámaso López Nuñez, a high-level leader of the Sinaloa cartel who was rumored to be Guzmán's successor after Guzmán's arrest in February 2014.

López Nuñez, originally from Sinaloa state, was a police officer in that state and later deputy director for security at Puente Grande prison in Jalisco state when "El Chapo" was there in the 1990s. He aided the kingpin in his escape in 2001.

"He's a former police officer, and he's also an attorney, and he's got a son that ... they call him 'Mini Lic,' or 'Mini Licenciado,' or 'Mini Attorney,' who apparently also is tied to the Sinaloa cartel [and] apparently works out of Baja California Sur," Vigil said.

In 2013, the US Treasury identified López Nuñez as a principal lieutenant of the Sinaloa cartel because of his alleged role in the cartel's drug trafficking and money laundering activities.

A US Treasury Department chart from January 2013 of top Sinaloa cartel officials. US Treasury Department

Because of his law degree, López Nuñez is nicknamed "El Licenciado."

The letter refers to him as such, suggesting he was in fact behind the attack. However, some reports of the incident say "El Mini Lic" — López Nuñez's son, Dámaso López Serrano— was the culprit. The younger López, 37, is reportedly the founder of Los Antrax, an armed wing of the Sinaloa cartel.

López Nuñez is the son of Dámaso López García, who was a member of the Institutional Revolutionary Party in Sinaloa. The PRI is also the party of Mexico's current president, Enrique Peña Nieto.

The link between the López family and the PRI has added to suspicions that the party is currently tied to drug trafficking — a belief bolstered by the party's involvement with the drug trade in the latter half of the 20th century, when it governed Mexico as a de facto one-party state.

The attack on Guzmán's sons and Zambada comes amid a spike in violence in Sinaloa state, which has picked up in the weeks since Guzmán's extradition in late January.

Twelve people were killed in the state over the weekend, with four people killed in Culiacan, the state capital, in two shootings 40 minutes apart.

In 72 hours between Sunday and Tuesday, 13 more people were slain in five shootouts between criminal groups.

The state's public security secretary, Gen. Genaro Robles Casillas, told the news agency EFE that the wave of violence was the result of fighting between factions of the Sinaloa cartel for control of the territory.

Police stand over a body at the site where a military convoy was ambushed with grenades and high-powered guns, killing five soldiers, in the city of Culiacan on September 30. AP Photo/Rashide Frias

"There's been a rash of killings in Culiacan," Vigil told Business Insider on Thursday. "I think there were quite a few murders. They estimate about 30 to 60 murders that have happened there in the last couple of days."

"El Chapo" Guzmán's sons also distributed a letter in October denying their involvement in a roadside ambush in Culiacan in which five soldiers were killed and several others were injured.

That attack was initially thought to be an effort to liberate a captured cartel member, but it is now suspected that one cartel faction launched it to attract law-enforcement attention to territory controlled by a rival faction.